Fix TOTAL row and % column output in diff mode

[pepsiman]

Fixes #361 and #335.

Before:

    FILE SIZE        VM SIZE
 --------------  --------------
  +203% +1.46Ki  [ = ]       0    [Unmapped]
  +100%     +48  +100%     +48    .rodata
  +100%      -8  +100%      -8    .ARM.exidx
   +50%      -8   +50%      -8    .fini
  +100%     -12  +100%     -12    .ARM.extab
   +99% -5.48Ki   +99% -5.48Ki    .text
  +100% +1.72Mi  +100% +1.72Mi    TOTAL

After:

    FILE SIZE        VM SIZE
 --------------  --------------
  +103% +1.46Ki  [ = ]       0    [Unmapped]
  +0.0%     +48  +0.0%     +48    .rodata
  -0.0%      -8  -0.0%      -8    .ARM.exidx
 -50.0%      -8 -50.0%      -8    .fini
  -0.0%     -12  -0.0%     -12    .ARM.extab
  -0.5% -5.48Ki  -0.5% -5.48Ki    .text
  -0.2% -4.00Ki  -0.3% -5.46Ki    TOTAL

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